1. Field of the Invention
The present invention relates to a driving method of a surface discharge type plasma display panel (PDP).
A PDP is commercialized as a wall-hung television set or a monitor of a computer, and the screen size thereof has reached 60 inches. In addition, a PDP is a digital display device comprising binary light emission cells and is suitable for displaying digital data, so it is expected as a multimedia monitor. In a market, a device having high resolution supporting a high quality digital image and being capable of displaying a bright image is desired.
2. Description of the Prior Art
In an AC type PDP, charge quantity (wall charge quantity) of a dielectric layer is controlled in accordance with contents of display in an addressing period, and then the wall charge is used for generating a display discharge plural times corresponding to a luminance value in a sustaining period. In the sustaining period, a sustaining voltage Vs having alternating polarities is applied across a pair of display electrodes. The sustaining voltage Vs satisfies the following inequality (1).VfXY−VwXY<Vs<VfXY  (1)
Here, Vfxy is a discharge start voltage between the display electrodes, and Vwxy is a wall voltage between the display electrodes. The application of the sustaining voltage Vs causes a display discharge only in cells having predetermined quantity of wall charge when a cell voltage (a sum of a drive voltage applied to the electrodes and the wall voltage) exceeds the discharge start voltage Vfxy. Since a usual application period is short such as a few microseconds, the light emission can be seen continuously.
A surface discharge format is adopted in an AC type PDP for a color display. In this surface discharge format, display electrodes to be an anode and a cathode in the display discharge are arranged in parallel on a front or rear substrate, and address electrodes are arranged in such a way to cross the display electrode pair. Also in the surface discharge type PDP, the display electrodes are connected with driving circuits by distributing display electrode terminals alternately in both sides (e.g., right and left sides) of a display screen in the order of electrode arrangement, as a usual method.
There are two forms of arrangement of the display electrodes for the surface discharge type. Hereinafter, one form is referred to as Form A and another form is referred to as Form B. In Form A, a pair of display electrodes is arranged for each row. The total number of the display electrodes is twice the number of rows n. In Form A, each row is independent of other rows when being controlled, so there is large flexibility of driving sequence. However, since an electrode gap between neighboring rows (also called a reverse slit) becomes a non-lighted area, utilization factor of the display screen is small. In Form B, display electrodes of the number of rows n plus one are arranged substantially at a constant pitch at the ratio of three per two rows. In Form B, neighboring display electrodes constitute an electrode pair for a surface discharge, and every display electrode gap becomes a surface discharge gap. Display electrodes except both ends of the arrangement relates to displays of an odd row and an even row. This Form B has an advantage from the viewpoints of high definition (a small row pitch), an efficient use of the display screen, and high resolution (increase of rows).
Conventionally, a PDP having an electrode structure of Form B is used for a display of an interlace format. In the interlace format, a half of rows in the entire screen is not used in each of odd and even fields. For example, even-numbered rows are not lighted in an odd field. Therefore, luminance in the interlace format is lower than that in the progressive format. In addition, the interlace format has another disadvantage in that flickers are conspicuous in a display of a still picture. The progressive format is suitable for a high quality display that is required for high quality image equipment such as a DVD or a HDTV.
If an appropriate addressing is performed for a PDP of Form B, a display of the progressive format can be realized. Namely, when a sustaining voltage Vs having alternating polarities is applied across the display electrodes in the same way as in the PDP of Form A, an odd row and an even row can be lighted at the same time. However, if the usual driving method is applied as it is, in which the neighboring display electrodes are biased alternately, directions of current flowing through the display electrodes upon the display discharge become the same in all display electrodes. When the directions of the current are the same, magnetic fields generated when electricity is supplied are strengthened by each other, resulting in a problem of EMI (electromagnetic interference) between the display screen and external equipment.
A driving method that is effective at reducing the electromagnetic interference in a PDP of Form A is disclosed in Japanese unexamined patent publication No. 10-3280. As disclosed in this publication, in the case of Form A, display electrodes to be biased are divided into right and left in such a way that a display electrode having a terminal at the left side of the display screen is biased in an odd row, while another display electrode having a terminal at the right side is biased in an even row, so that the direction of current in the odd row becomes opposite to that in the even row. When the directions of current are opposite to each other, magnetic fields are canceled by each other. If an image to be displayed has the same number of lighted cells between neighboring rows, the magnetic fields are completely canceled by each other. However, this conventional technique cannot be applied to a PDP of Form B, because neighboring odd and even rows share a display electrode in Form B, so that the direction of current cannot be set independently for each row.